RP 07 Measuring RoR

• What is meant by 'rate of reaction'?

  The change in concentration of reactants/products over time
• How can rate of reaction be measured?

  • Initial rates method e.g iodine clock reaction
  • A continuous monitoring method e.g measuring the volume of gas released in a reaction over time
• What is an initial rates method?

  Measuring initial rate of reaction for multiple different concentrations to observe how rate of reaction varies
• What is an example of an initial rates method?

  The 'Iodine Clock' experiment
• What happens to the I2 produced in the 'Iodine Clock' experiment?

  The I2 produced reacts with thiosulfate ions, and excess I2 reacts with starch to form a blue-black solution.
• How can you determine the order with respect to iodide ions in the 'Iodine Clock' experiment?

  You can vary the concentration of \([\text{I}^-]\) and time how long it takes for the blue-black color to appear.
• What are some issues with the 'Iodine Clock' experiment?

  Some low \([\text{I}^-]\) concentrations may take too long to react, and there may be delayed stopwatch reactions.
• What is a continuous monitoring method in chemical experiments?

  It involves measuring the change in concentration of a reactant or product over time as the reaction progresses.
• Give an example of a continuous monitoring method.

  Add a 6 cm strip of magnesium ribbon into a conical flask containing HCl and measure the volume of hydrogen gas produced.
• How would you analyze the data from the magnesium and HCl experiment?

  • Plot a graph of volume of hydrogen gas produced (y-axis) against time (x-axis).
  • Draw a line of best fit for each concentration of HCl.
  • Draw a tangent at \( t = 0s \) for each line.
  • Calculate the gradient of each tangent to deduce the rate of each reaction.
  • Compare the calculated rate values.
• What should the setup for the magnesium and HCl experiment look like?

  The magnesium ribbon should be placed in a conical flask with HCl, and a bung should be used to prevent gas escape.
• What are some issues with the magnesium and HCl experiment?

  Some gas may escape before the bung is added, and magnesium strips may vary in mass and surface area affecting the reaction rate.
• How do you prevent gas from escaping in the magnesium and HCl experiment?

  Place the solid reactant upright inside a sample tube in the conical flask and tip the tube over to start the reaction.